Papers by Author: Ewald Werner

Abstract: A method is presented by which all components of Fij(ϕ, ψ, hkl) belonging to the same measurement direction and reflection can be determined. The neutron measurements are to be done with a single specimen, shaped as a cuboctahedron. An apparatus for producing a compressive stress state in the specimen is needed. It must be small enough to fit into the neutron goniometer and to allow movement of the goniometer to all Eulerian angles. Using this set-up the tensors F(ϕ, ψ, hkl) can be measured for any ϕ, ψ and (hkl).

Abstract: Mechanical and thermal treatments during the manufacturing process inevitably cause the accumulation of residual stresses in parts consisting of materials with complex microstructures. Neutron diffraction is particularly well suited to determine residual stress distributions within the bulk of the component. Due to the nature of a diffraction experiment an inextricable mixture of type I and II residual stresses is measured. The accumulation of type II stresses (microstresses) is strongly related to the microstructure. The impact of changes in the microstructure on neutron diffraction experiments has been investigated on Inconel 718 (IN718) samples.

Abstract: Since the early 1960s hot isostatic pressing (HIP) was used to improve the quality of castings made of various alloys. The closure of pores, originating from the casting process, is considered as the main source of these improvements. For the aluminium alloy Al-9Si-3Cu specimens for tensile testing were machined from castings either squeeze casted and heat treated to T4 and T6 conditions or investment casted. The effect of HIP on density, roughness and mechanical properties was investigated. The density and roughness of the squeeze casted specimens did not change remarkably and their tensile strength became worse, because the initial heat-treatment-state was destroyed by HIP. The investment casted specimens became denser and roughness became worse due to closure of pores near the surface. Although roughness after HIP was higher than in the initial state, tensile strength was improved significantly by HIP, because of closure of the pores in the specimen.

Abstract: The forging die material, a high strength steel designated W513 is considered in this paper. A fatigue damage model, based on thermodynamics and continuum damage mechanics, is constructed in which both the previous damage and the loading sequence are considered. The unknown material parameters in the model are identified from low cycle fatigue tests. Damage evolution under multi-level fatigue loading is investigated. The results show that the fatigue life is closely related to the loading sequence. The fatigue life of the materials with low fatigue loading first followed by high fatigue loading is longer than that for the reversed loading sequence.